(a) Field of the Invention
The present invention relates to a field emission display, and more particularly, to a field emission display having a carbon-based emitter.
(b) Description of the Related Art
A field emission display (FED) uses a cold cathode as the source for emitting electrons. The overall quality of the FED depends on the characteristics of emitters, which is for an electron emission layer. The first FEDs utilized emitters made mainly of molybdenum (Mo). Subsequently, Spindt-type metal tip emitters were developed. An example of this prior art technology is disclosed in U.S. Pat. No. 3,789,471, which is related to a display system having a field emission cathode.
However, a semiconductor fabrication process is used to manufacture the FED having a metal tip emitter. Such process includes photolithography and etching processes to form a hole that accommodates an emitter as well as deposition of molybdenum to form metal tips. This requires not only advanced technologies but also expensive equipment, increasing the manufacturing costs. These factors make mass production of these types of FEDs difficult.
Accordingly, much research has been done to form emitters in a flat configuration that enables electron emission at a low voltage (around 10xe2x96xa150V), and simple manufacture. It is known that carbon-based materials, for example graphite, diamond, DLC (diamond-like carbon), C60 (Fullerene), or CNT (carbon nanotube), are suitable for planar emitters. In particular, it is believed that CNT, is the ideal material for emitters in field emission displays because of its relatively low driving voltage. U.S. Pat. Nos. 6,062,931 and 6,097,138 disclose cold cathode field emission displays that are related to this area of FEDs using CNT technology.
The FEDs disclosed in these patents employ a triode structure in which the gate electrode is provided between the cathode electrode and an anode electrode.
However, when the triode structured FED adopts carbon-based material, like carbon nanotubes, as emitting material, it is difficult to precisely form the emitters into the gate holes of the insulation layer between cathode electrode and gate electrode. In particular, it is extremely difficult to provide the paste in the minute holes for formation of the emitters using a printing process.
There have been recent efforts to solve these problems by different arrangement of electrodes. U.S. Patent Application Publication Pub. No. 2001/0006232 A1 discloses an FED that provides a gate electrode between a substrate and a cathode electrode. In this type of FED, the emitters of carbonbased materials may be easily formed by printing process, since the emitters are provided on the uppermost portion of the substrate as the gate electrode has changed its position. As a result, mass production became possible.
Various positions where to locate the gate eletrode and the emitter and their relationships have been disclosed in the U.S. patent application Ser. No. 09/967,936 filed Oct. 2, 2001, which was assigned to the same assignee of the present Application, and which is hereby incorporated by reference.
However, it is necessary to apply a high voltage to the gate electrode, in order to form a sufficient electrical field for electron emission, since the gate electrode is covered by an insulation layer. Otherwise, the cathode electrode should have large spacing between each other, that causes charge accumulation in insulation layer and abnormal irradiation of phosphor.
The present invention has been made in an effort to solve the above problems.
It is an object of the present invention to provide a field emission display that achieves good picture quality while obtaining sufficient field emission without increasing a voltage to drive a gate electrode.
To achieve the above object, the present invention provides a field emission display including a first substrate; a plurality of gate electrodes formed on the first substrate in a predetermined pattern; an insulation layer formed over the entire surface of the first substrate covering the gate electrodes; a plurality of cathode electrodes formed on the insulation layer in a predetermined pattern, a plurality of emitters being formed on the cathode electrodes; a plurality of counter electrodes which are electrically connected to the gate electrodes making an electric field directed toward the emitters formed on the insulation layer at a predetermined distance from the emitters, a second substrate provided at a predetermined distance from the first substrate and sealed in a vacuum state with the first substrate; an anode electrode formed on a surface of the second substrate opposing the first substrate; and a plurality of phosphor layers formed over the anode electrode in a predetermined pattern.
The electrical connection between the counter electrodes and the gate electrodes is realized by the holes through the insulation layer. The connection part may be made of the same material as the counter electrodes or other conductive materials.
It is preferable that a suitable distance between counter electrodes and the cathode electrodes be maintained to form an electric field for optimal electron emission. In addition, it is preferable that the counter electrodes are higher than the cathode electrodes to form an electric field for optimal electron emission.
Also, it is preferable that surfaces of the counter electrode and emitter facing each other are unevenly formed in a saw-tooth configuration or in a rounded formation.